I recently purchased a new (nothing fancy Kalloy) seat post to accommodate a low profile saddle. I took measurements with my dial calipers, looked it up on Sheldon Brown's database, and most importantly looked at the previous seat post (although there was some rust by the size engraving), and everything pointed to 26.8mm.
I went to install it, deburred the frame, used a ton of grease, and it was nearly impossible to get in. I ended up sanding some material off the seat post and then with turning motions (using the saddle for leverage) was finally able to get the seat post in (albeit maybe a few mm higher than I want it). I gave up trying to adjust it any more.
Now, on longer rides I'm getting a little pain in the elbows, and I attribute this to the slightly higher saddle height elongating my elbows making it harder for them to flex and absorb shock.
Later I was looking at the catalog page (for something unrelated to the seat post) for my bike and it said SR-CRE 100 Microadjusting 26.6 seat post.
1) Could it be possible my bike really takes a 26.6? I'm assuming this is why I had so much trouble (when the other seat post would move freely around).
2) Could I purchase the 26.6 and use it in my bike? Will the tube now be overextended to fit a 26.6?
3) Did I permanently damage my steel double butted tubing? It doesn't look deformed and I never hammered to get it in, just twisted back and forth and stopped when it got too hot.
I would like to go to the 26.6 so that I can adjust further (sometimes even during rides) without having to swear profusely.
It doesn't have a clamp, it uses a bolt through the frame to secure the seat post.
Looks like this: